Millimeter-sized single crystals of LaFeAsO, LaFeAsO1−xFx, and LaFe1−xCoxAsO were grown in NaAs flux at ambient pressure. The detailed growth procedure and crystal characterizations are reported. The as-grown crystals have typical dimensions of 3×4×0.05–0.3 mm3 with the crystallographic c-axis perpendicular to the plane of the platelike single crystals. Various characterizations confirmed the high quality of our LaFeAsO crystals. Co and F were introduced into the lattice leading to superconducting LaFe1−xCoxAsO and LaFeAsO1−xFx single crystals, respectively. This growth protocol is expected to be broadly applicable to grow other RMAsO (R=rare earth, M=transition metal) compounds.

Large high-quality single crystals of hole-doped iron-based superconductor (Ba${}_{1$-${}x}$K${}_{x}$)Fe${}_{2}$As${}_{2}$ were grown over a broad composition range $0.22$\le${}x$\le${}1$ by inverted temperature gradient method. We found that high soaking temperature, fast cooling rate, and an adjusted temperature window of the growth are necessary to obtain single crystals of heavily K-doped crystals ($0.65$\le${}x$\le${}0.92$) with narrow compositional distributions as revealed by sharp superconducting transitions in magnetization measurements and close to 100% superconducting volume fraction. The crystals were extensively characterized by x-ray and compositional analysis, revealing monotonic evolution of the $c$-axis crystal lattice parameter with K substitution. Quantitative measurements of the temperature-dependent in-plane resistivity $$\rho${}(T)$ found doping-independent, constant within error bars, resistivity at room temperature, $$\rho${}(300\phantom{\rule{0.28em}{0ex}}\mathrm{K})$, in sharp contrast with the significant doping dependence in electron and isovalent substituted BaFe${}_{2}$As${}_{2}$ based compositions. The shape of the temperature-dependent resistivity, $$\rho${}(T)$, shows systematic doping-evolution, being close to ${T}^{2}$ in overdoped and revealing significant contribution of the $T$-linear component at optimum doping. The slope of the upper critical field, $d{H}_{c2}/dT$, scales linearly with ${T}_{c}$ for both $H$\parallel${}c$, ${H}_{c2,c}$, and $H$\parallel${}ab$, ${H}_{c2,ab}$. The anisotropy of the upper critical field $$\gamma${}$\equiv${}{H}_{c2,ab}/{H}_{c2,c}$ determined near zero-field ${T}_{c}$ increases from $$\sim${}$2 to 4\char21{}5 with increasing K doping level from optimal $x$\sim${}0.4$ to strongly overdoped $x=1$.

The structural and magnetic phase transitions have been studied on NdFeAsO single crystals by neutron and x-ray diffraction complemented by resistivity and specific-heat measurements. Two low-temperature phase transitions have been observed in addition to the tetragonal-to-orthorhombic transition at $T_S\sim 142\text{K}$ and the onset of antiferromagnetic (AFM) Fe order below $T_N\sim 137\text{K}$. The Fe moments order AFM in the well-known stripelike structure in the $\left(ab\right)$ plane but change from AFM to ferromagnetic (FM) arrangement along the $c$ direction below $T^{\ast }\sim 15\text{K}$ accompanied by the onset of Nd AFM order below $T_{\text{Nd}}\sim 6\text{K}$ with this same AFM configuration. The iron magnetic order-order transition in NdFeAsO accentuates the Nd-Fe interaction and the delicate balance of $c$-axis exchange couplings that results in AFM in LaFeAsO and FM in CeFeAsO and PrFeAsO.

Fe-Si electric steel is the most widely used soft magnetic material in electric machines and transformers. Increasing the silicon content from 3.2 wt.% to 6.5 wt.% brings about large improvement in the magnetic and electrical properties. However, 6.5 wt.% silicon steel is inherited with brittleness owing to the formation of B2 and D0₃ ordered phase. To obtain ductility in Fe-6.5wt.% silicon steel, the ordered phase has to be bypassed with methods like rapid cooling. In present paper, the effect of cooling rate on magnetic and mechanical properties of Fe-6.5wt.% silicon steel is studied by tuning the wheel speed during melt spinning process. The cooling rate significantly alters the ordering and microstructure, and thus the mechanical and magnetic properties. X-ray diffraction data shows that D0₃ ordering was fully suppressed at high wheel speeds but starts to nucleate at 10m/s and below, which correlates with the increase of Young’s modulus towards low wheel speeds as tested by nanoindentation. The grain sizes of the ribbons on the wheel side decrease with increasing wheel speeds, ranging from ∼100 μm at 1m/s to ∼8 μm at 30m/s, which lead to changes in coercivity.

We report on the crystal and magnetic structures and magnetic and transport properties of ${\mathrm{SrMnSb}}_2$ single crystals grown by the self-flux method. Magnetic susceptibility measurements reveal an antiferromagnetic (AFM) transition at $T_{\mathrm{N}}=295\left(3\right)$ K. Above $T_{\mathrm{N}}$, the susceptibility slightly increases and forms a broad peak at $T\sim 420$ K, which is a typical feature of two-dimensional magnetic systems. Neutron diffraction measurements on single crystals confirm the previously reported C-type AFM structure below $T_{\mathrm{N}}$. Both de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) effects are observed in ${\mathrm{SrMnSb}}_2$ single crystals. Analysis of the oscillatory component by a Fourier transform shows that the prominent frequencies obtained by the two different techniques are practically the same within error regardless of sample size or saturated magnetic moment. Transmission electron microscopy (TEM) reveals the existence of stacking faults in the crystals, which result from a horizontal shift of Sb atomic layers suggesting possible ordering of Sb vacancies in the crystals. Increase of temperature in susceptibility measurements leads to the formation of a strong peak at $T\sim 570$ K that upon cooling under magnetic field the susceptibility shows a ferromagnetic transition at $T_{\mathrm{C}}\sim 580$ K. Neutron powder diffraction on crushed single crystals does not support a ferromagnetic phase above $T_{\mathrm{N}}$. Furthermore, x-ray magnetic circular dichroism (XMCD) measurements of a single crystal at the $L_{2,3}$ edge of Mn shows a signal due to induced canting of AFM moments by the applied magnetic field. All evidence strongly suggests that a chemical transformation at the surface of single crystals occurs above 500 K concurrently producing a minute amount of ferromagnetic impurity phase.